The present invention relates to an internal combustion fastener driving tool including a handle system that is coupled to and supports a drive system, a magazine, and a nose piece. The fastener driving system is operable through an internal combustion driven piston. The drive system includes a driver body which includes a piston housing in which a piston is slideably housed. A driving member is coupled to the piston. A combustion chamber is defined by the driver body, piston housing, and piston. The piston and driving member are axially arranged and configured within the piston housing to drive a fastener upon combustion of a metered amount of gaseous fuel in the combustion chamber.
A preferred fastener driving tool includes a fuel metering system arranged and configured to provide a metered amount of gaseous fuel. A preferred fuel metering system includes a port for receiving gaseous fuel that is defined by the tool, a regulator that is in fluid communication with the port, and a shuttle valve. A preferred shuttle valve includes a metering chamber housing, a metering chamber defined by the metering chamber housing, a combustion check valve, and one gating valve. The metering chamber and gating valve are arranged and configured to provide asynchronous fluid communication between the metering chamber and combustion chamber, or between the metering chamber and the regulator. The combustion check valve is arranged and configured to prevent fluid flow from the combustion chamber to the metering chamber.